Blender Git Loki

Add RNA for brush capabilities (sculpt-only for now.)

Added a new RNA-only nested structure, Brush.SculptCapabilities. It
contains read-only properties that use the current sculpt tool (and
occasionally other brush properties) to determine whether some feature
is available.

For example, the grab and snake-hook brushes don't support the
strength property. Querying brush.sculpt_capabilities.has_strength
will return false only if one of these brushes is selected.